A London-born boy has become the first millennial saint, in a ceremony steeped in an ancient ritual presided over by Pope Leo on Sunday.

In his short life, Carlo Acutis created websites documenting “miracles” as a means of spreading Catholic teaching, leading some to nickname him God’s influencer.

His canonisation had been due in late April, but was postponed following the death of Pope Francis.

More than a million people are estimated to have made a pilgrimage to the Italian hilltop town of Assisi where Carlo’s body lies, preserved in wax.

But there is another pilgrimage site associated with Carlo Acutis that has seen an increase in visitors since it was announced that he was to be made a saint – Our Lady of Dolours Church in London.

The font at the back of the Roman Catholic church in the Chelsea area was where Carlo was baptised as a baby in 1991.

To the side of the church an old confession booth has been converted into a shrine to him. In it, a relic holder contains a single strand of Carlo’s hair.

“His family were in finance and they were working really temporarily in London,” says Father Paul Addison, a friar at the church.

“Although they didn’t use the church much, they decided to come and ask to have the child baptised. So Carlo was a flash, a very big flash, in the life of the parish community,” he says.

Carlo was not yet six months old when his parents moved back to their home country of Italy, and he spent the rest of his life in Milan.

There, he was known for a love of technology and is said to have enjoyed playing video games.

While some who knew Carlo Acutis say he did not appear to be especially devout, as a teenager he did create a website – pages of which are now framed at the church in Chelsea – in which miracles were documented.

But he died of leukaemia aged just 15.

In the years after his death, Carlo’s mother, Antonia Salzano, visited churches around the world to advocate for him to be a saint.

As part of the process, it had to be proved her son had performed “miracles”.

“The first miracle, he did the day of the funeral,” says Carlo’s mother.

“A woman with breast cancer prayed (for) Carlo and she had to start chemotherapy and the cancer disappeared completely,” she explains.

Pope Francis attributed two miracles to Carlo Acutis and so the test was passed and he was due to be made a saint on 27 April.

But Pope Francis died during the preceding week.

Some followers who had travelled to Rome for the canonisation instead found themselves among the tens of thousands of mourners at the late pontiff’s funeral – Diego Sarkissian, a young Catholic from London, was one of them.

He says he feels a connection to Carlo Acutis and is excited by his canonisation.

“He used to play Super Mario video games on the old Nintendo consoles and I’ve always loved video games,” Mr Sarkissian says.

“The fact that you can think of a saint doing the same things [as you], wearing jeans, it feels so much closer than what other saints have felt like in the past,” he says.

Approval for someone to become a saint can take decades or even centuries, but there is a sense that the Vatican fast-tracked Carlo Acutis’ canonisation as a means of energising and inspiring faith in young people.

The Catholic Church will be hoping Sunday’s events do just that.